Deep ultraviolet ray having a wavelength of 200 to 350 nm is known as having not only a function to act on nucleic acid which is protoplasm of bacteria to deprive them of proliferating ability, but also a function to destroy protoplasm to kill bacteria. An ultraviolet ray sterilizing apparatus which performs sterilization on bacteria by irradiating bacteria with ultraviolet ray having such functions are practically used. As a light source used in the ultraviolet ray sterilizing apparatus, a low pressure mercury lamp (so-called sterilization lamp) which emits light having a wavelength of 253.7 nm (resonance line of mercury) generated due to discharge of a low-pressure (approximately 0.1 Pa) mercury vapor is generally known. The sterilization lamp is widely used in various fields.
An air purifier having a sterilization ability by means of the sterilization lamp is also known. For example, as a stationary or wall-hanging type air purifier for purifying air in a living space such as a room, an air purifier including a body provided with inlet and outlet ports, the body including an air blowing unit including a centrifugal fan and a fan motor shaft-fastening the centrifugal fan, for forming an air passage in the body, wherein a filter and an ultraviolet ray sterilizing apparatus are provided in the order mentioned from an upstream side of the air passage, is known (see Patent Literatures 1 and 2). The above-described ultraviolet ray sterilizing apparatus is provided with a sterilization lamp (s) arranged on a center portion of a unit case made of a metal box, and with openings on the front side and back side of the unit case. The sterilizing apparatus is configured in such a way that air passes through the inside of the unit case, and sterilization is carried out by ultraviolet ray which irradiates the air which passes through the inside of the unit case. In the ultraviolet ray sterilizing apparatus used in a conventional air purifier as above, following measures are taken in order to prevent degradation of resin materials and adverse effects on human body that are caused by leakage of the ultraviolet ray. That is: firstly, in order to prevent ultraviolet ray from reflecting on the inner surface of the unit case, the inner surface is coated by a fluororesin coating material, or the inner surface itself is configured by an electrogalvanized steel sheet (SECC steel sheet) (Patent Literatures 1 and 2); secondly, in order to prevent leakage of ultraviolet ray from the opening, a cut and raised part is formed on the opening of the unit case (Patent Literature 1), or an ultraviolet ray-blocking member having a honeycombed shape, to the inner surface of which a ultraviolet ray absorbing coating material is applied, is attached (Patent Literature 2).